Mepazine hydrochloride is primarily used in the field of psychiatry as a tranquilizer and antipsychotic agent. It is effective in managing symptoms of various mental health disorders, particularly schizophrenia and other psychotic conditions. The compound helps in reducing agitation, anxiety, and hyperactivity in patients, promoting a calming effect. It is also utilized in some cases to alleviate severe nausea and vomiting, especially when associated with psychiatric treatments. Additionally, mepazine hydrochloride has been explored for its potential in managing certain types of chronic pain, though this application is less common. Its use requires careful monitoring due to potential side effects and interactions with other medications.